This is a bullaun stone, a type of carved rock found at many early Irish religious sites, where the rounded hollow was worn or deliberately cut, possibly for ritual use, the grinding of pigments, or the collection of water believed to carry curative properties. What makes this particular example quietly arresting is its position, well outside the main monastic enclosure and exposed to the sea, and the fact that beside the bullaun depression someone also carved a cross, its arms and shaft formed not by simple incision but by a series of deep oval depressions linked together with shallow grooves.

Illauntannig is the largest of the Magharee Islands, and the Early Christian settlement it contains is remarkably complete. Behind a strong cashel wall, the drystone enclosure that defines the monastic boundary, there are two small oratories, three bee-hive huts of the corbelled stone type characteristic of early Irish monasticism, a souterrain, three leachts (low stone platforms associated with commemoration of the dead), a burial ground, and a stone cross. Finds from within the enclosure include three cross-slabs, a hand-bell, fragments of five quern-stones, and a first bullaun stone. The shoreline boulder is a second, and its placement roughly 100 metres to the south of the cashel, right at the sea's edge, sets it apart from the more sheltered religious furniture inside the walls. Whether it was always intended to stand in that liminal, tidal position, or whether centuries of coastal shift have brought the water closer, is not recorded.